The present invention relates to the art of diagnostic computed tomography (CT) imaging. It finds particular application in conjunction with cardiac gated spiral CT scanners, and will be described with particular reference thereto. However, it is to be appreciated that the present invention is also amenable to other like applications.
In typical spiral or helical CT scanning, an x-ray source or tube emits a fan beam of radiation as it rotates continuously around an examination region as a patient support table moves therethrough at a constant, linear velocity. Detectors positioned across the examination region from the x-ray tube convert x-rays which traverse the patient into corresponding electronic data. The collected data effectively represents a helical path of constant pitch through the patient. The helical data is reconstructed into a volumetric image representation, typically a series of consecutive thin slice images of a region of interest of the patient. See for example, U.S. Pat. Nos. 5,544,212; 5,485,493; 5,262,946; and, 5,396,418; all commonly assigned and incorporated by reference herein.
Furthermore, a number of methods are aimed at reconstructing cardiac images with reduced motion artifacts. For example: a prospective electrocardiogram (ECG) gated method with axial slice CT acquisition has been used to reconstruct cardiac images, as shown in U.S. Pat. No. 5,751,782 to Yoshitome; a retrospective ECG-gated CT data acquisition and reconstruction technique using spiral CT is also known; a prospective ECG-gated technique with spiral CT data acquisition for imaging only the diastolic phase of the heart is known; and, a prospective ECG-gated technique is known which employs a scan time of 100 ms/slice in an electron beam CT (EBCT) scanner such as the one described in U.S. Pat. No. 4,573,179 to Rutt. However, the above techniques have failed to provide a generalized scheme for cardiac reconstruction of any selected cardiac phase for various heart rates and/or different gantry speeds and configurations. In addition, the above techniques suffer from various drawbacks and are therefore less than ideal in certain aspects for diagnostic cardiac imaging.
For example, one drawback of the technique employed in U.S. Pat. No. 5,751,782 and other such cardiac gated axial slice systems is that they use multiple rotations for reconstructing a single slice, and hence, have a longer scan time. A disadvantage of retrospective ECG-gated CT data reconstruction is that processor resources and time is consumed in the processing of too many images. Additionally, the prior art techniques do not consider advantageous multi-ring scanner configurations. The aforementioned prospective ECG-gated technique with spiral CT acquisition is less than ideal in that it is limited to a given phase of the heart and does not demonstrate the detector configuration, scanner speed, and imaging protocol best for removing motion artifacts.
Use of EBCT imaging in diagnostic cardiac applications also has certain drawbacks. First of all, it is primarily a research tool and it is not as widely available for clinical applications as conventional spiral CT scanners. In addition, EBCT scanners are generally much more expensive. Often, EBCT scanners have poor image quality and their z-axis resolution limits usefulness.
The present invention contemplates a new and improved cardiac gated spiral CT imaging apparatus and technique which overcomes the above-referenced problems and others.